U.S. patent application number 14/358007 was filed with the patent office on 2014-10-16 for method and apparatus for transmitting control information in wireless communication system.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTORNICS INC.. Invention is credited to Hakseong Kim, Hanbyul Seo, Inkwon Seo.
Application Number | 20140307700 14/358007 |
Document ID | / |
Family ID | 48290339 |
Filed Date | 2014-10-16 |
United States Patent
Application |
20140307700 |
Kind Code |
A1 |
Seo; Inkwon ; et
al. |
October 16, 2014 |
METHOD AND APPARATUS FOR TRANSMITTING CONTROL INFORMATION IN
WIRELESS COMMUNICATION SYSTEM
Abstract
A method for enabling a base station to transmit control
information in a wireless communication system according to one
embodiment of the present invention, comprises a step of
transmitting an enhanced physical downlink channel (E-PDCCH) for a
terminal using at least one physical resource block pair among a
plurality of physical resource block pairs for transmitting the
E-PDCCH, wherein the plurality of physical resource block pairs
include one or more physical resource block pair sets, and a
parameter related to a demodulation reference signal for the
E-PDCCH is set with respect to each physical resource block pair
set.
Inventors: |
Seo; Inkwon; (Anyang-si,
KR) ; Seo; Hanbyul; (Anyang-si, KR) ; Kim;
Hakseong; (Anyang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTORNICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
48290339 |
Appl. No.: |
14/358007 |
Filed: |
November 13, 2012 |
PCT Filed: |
November 13, 2012 |
PCT NO: |
PCT/KR2012/009544 |
371 Date: |
May 13, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61559139 |
Nov 13, 2011 |
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61598302 |
Feb 13, 2012 |
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61650480 |
May 23, 2012 |
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61661331 |
Jun 18, 2012 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04L 5/0051 20130101;
H04W 72/0406 20130101; H04L 5/0053 20130101; H04W 72/042 20130101;
H04L 5/0048 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04L 5/00 20060101 H04L005/00 |
Claims
1. A method for transmitting control information by a base station
in a wireless communication system, the method comprising:
transmitting an enhanced physical downlink channel (E-PDCCH) to a
user equipment, using at least one or more physical resource block
(PRB) pairs among a plurality of PRB pairs for E-PDCCH
transmission, wherein the plurality of PRB pairs include one or
more PRB pair sets, and wherein a parameter associated with a
demodulation reference signal for the E-PDCCH is configured with
respect to each of the one or more PRB pair sets.
2. The method according to claim 1, wherein the one or more PRB
pair sets includes one or more sets among one or more PRB pair sets
for localized transmission and one or more PRB pair sets for
distributed transmission.
3. The method according to claim 2, wherein the parameter is a
parameter for determining an initial value of a scrambling sequence
needed to generate the demodulation reference signal.
4. The method according to claim 2, wherein the parameter for
determining the initial value of the scrambling sequence is
transmitted to the user equipment through higher layer
signaling.
5. The method according to claim 2, wherein the parameter is a
plurality of antenna ports.
6. The method according to claim 5, wherein information regarding
the plural antenna ports is transmitted to the user equipment
through higher layer signaling.
7. The method according to claim 1, wherein the plurality of PRB
pairs include four minimum resource units for E-PDCCH
transmission.
8. The method according to claim 5, wherein the antenna ports are
respectively associated with minimum resource units for E-PDCCH
transmission.
9. The method according to claim 1, wherein only partial antenna
ports among preset antenna ports for the PRB pairs are used when
resources available for the E-PDCCH in the physical resource pairs
decreases.
10. A base station in a wireless communication system, the base
station comprising: a transmission module; and a processor, wherein
the processor transmits an enhanced physical downlink channel
(E-PDCCH) to a user equipment, using at least one or more physical
resource block (PRB) pairs among a plurality of PRB pairs for
E-PDCCH transmission, wherein the plurality of PRB pairs include
one or more PRB pair sets, and wherein a parameter associated with
a demodulation reference signal for the E-PDCCH is configured with
respect to each of the one or more PRB pair sets.
11. The method according to claim 10, wherein the one or more PRB
pair sets includes one or more sets among one or more PRB pair sets
for localized transmission and one or more PRB pair sets for
distributed transmission.
12. The method according to claim 11, wherein the parameter is a
parameter for determining an initial value of a scrambling sequence
needed to generate the demodulation reference signal.
13. The method according to claim 12, wherein information regarding
to the initial vale of the scrambling sequence is transmitted to
the user equipment through higher layer signaling.
14. The method according to claim 11, wherein the parameter is a
plurality of antenna ports.
15. The method according to claim 14, wherein information related
to the plural antenna ports is transmitted to the user equipment
through higher layer signaling.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system and, more particularly, to a method and apparatus for
transmitting an enhanced physical downlink channel (E-PDCCH) and a
demodulation reference signal (DMRS) for the E-PDCCH.
BACKGROUND ART
[0002] Wireless communication systems have been widely deployed in
order to provide various types of communication services such as
voice or data services. Generally, a wireless communication system
is a multiple access system capable of supporting communication
with multiple users by sharing available system resources
(bandwidth, transmit power, etc.). Multiple access systems include,
for example, a code division multiple access (CDMA) system, a
frequency division multiple access (FDMA) system, a time division
multiple access (TDMA) system, an orthogonal frequency division
multiple access (OFDMA) system, a single-carrier frequency division
multiple access (SC-FDMA) system, and a multi-carrier frequency
division multiple access (MC-FDMA) system.
DISCLOSURE
Technical Problem
[0003] The present invention discloses embodiments associated with
the relationship between a DMRS parameter and a resource, during
E-PDCCH transmission and DMRS transmission for an E-PDCCH, in
transmitting control information.
[0004] The technical objects that can be achieved through the
present invention are not limited to what has been particularly
described hereinabove and other technical objects not described
herein will be more clearly understood by persons skilled in the
art from the following detailed description.
Technical Solution
[0005] In a first technical aspect of the present invention,
provided herein is a method for transmitting control information by
a base station in a wireless communication system, the method
including transmitting an enhanced physical downlink channel
(E-PDCCH) to a user equipment, using at least one or more physical
resource block (PRB) pairs among a plurality of PRB pairs for
E-PDCCH transmission, wherein the plurality of PRB pairs include
one or more PRB pair sets, and wherein a parameter associated with
a demodulation reference signal for the E-PDCCH is configured with
respect to each of the one or more PRB pair sets.
[0006] In a second aspect of the present invention, provided herein
is a base station in a wireless communication system, the base
station including a transmission module and a processor, wherein
the processor transmits an enhanced physical downlink channel
(E-PDCCH) to a user equipment, using at least one or more physical
resource block (PRB) pairs among a plurality of PRB pairs for
E-PDCCH transmission, wherein the plurality of PRB pairs include
one or more PRB pair sets, and wherein a parameter associated with
a demodulation reference signal for the E-PDCCH is configured with
respect to each of the one or more PRB pair sets.
[0007] The first and second technical aspects of the present
invention may include the followings.
[0008] The one or more PRB pair sets may include one or more sets
among one or more PRB pair sets for localized transmission and one
or more PRB pair sets for distributed transmission. The parameter
may be a parameter for determining an initial value of a scrambling
sequence needed to generate the demodulation reference signal.
Information regarding the initial vale of the scrambling sequence
may be transmitted to the user equipment through higher layer
signaling.
[0009] The parameter may be a plurality of antenna ports.
Information regarding the plural antenna ports is transmitted to
the user equipment through higher layer signaling.
[0010] The plurality of PRB pairs may include four minimum resource
units for E-PDCCH transmission. The antenna ports may be
respectively associated with minimum resource units for E-PDCCH
transmission.
[0011] When resources available for the E-PDCCH in the physical
resource pairs decreases, only partial antenna ports among preset
antenna ports for the PRB pairs may be used.
Advantageous Effects
[0012] According to the present invention, transmission of control
information can be efficiently supported by defining the
relationship between a DMRS parameter and a resource.
[0013] Effects according to the present invention are not limited
to what has been particularly described hereinabove and other
advantages not described herein will be more clearly understood by
persons skilled in the art from the following detailed description
of the present invention.
DESCRIPTION OF DRAWINGS
[0014] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention.
[0015] FIG. 1 is a view illustrating the structure of a radio
frame.
[0016] FIG. 2 is a view illustrating a resource grid in a downlink
slot.
[0017] FIG. 3 is a view illustrating the structure of a downlink
subframe.
[0018] FIG. 4 is a view illustrating the structure of an uplink
subframe.
[0019] FIG. 5 is a view explaining a search space.
[0020] FIG. 6 is a view explaining reference signals.
[0021] FIGS. 7 and 8 are views explaining demodulation reference
signals.
[0022] FIGS. 9 to 14 are view explaining the relationship between
demodulation reference signal parameters and resources according to
embodiments of the present invention.
[0023] FIG. 15 is a view illustrating transmitting and receiving
devices.
BEST MODE FOR CARRYING OUT THE INVENTION
[0024] The embodiments of the present invention described
hereinbelow are combinations of elements and features of the
present invention. The elements or features may be considered
selective unless otherwise mentioned. Each element or feature may
be practiced without being combined with other elements or
features. Further, an embodiment of the present invention may be
constructed by combining parts of the elements and/or features.
Operation orders described in embodiments of the present invention
may be rearranged. Some constructions or features of any one
embodiment may be included in another embodiment and may be
replaced with corresponding constructions or features of another
embodiment.
[0025] In the present disclosure, the embodiments of the present
invention are described based on a data transmission and reception
relationship between a base station (BS) and a terminal. The BS is
a terminal node of a network, which directly communicates with the
terminal. A specific operation described as performed by the BS may
be performed by an upper node of the BS.
[0026] In other words, it is apparent that, in a network comprised
of a plurality of network nodes including a BS, various operations
performed for communication with a terminal may be performed by the
BS, or network nodes other than the BS. The term BS may be replaced
with the terms fixed station, Node B, evolved Node B (eNode B or
eNB), access point (AP), transmission point, etc. The term relay is
used interchangeably with relay node (RN), relay station (RS), etc.
The term terminal may be replaced with the terms user equipment
(UE), mobile station (MS), mobile subscriber station (MSS),
subscriber station (SS), etc.
[0027] Specific terms used in the following description are
provided to aid in understanding of the present invention. These
specific terms may be replaced with other terms within the scope
and spirit of the present invention.
[0028] In some cases, to prevent the concept of the present
invention from being ambiguous, structures and apparatuses of the
known art will be omitted, or will be shown in the form of a block
diagram based on main functions of each structure and apparatus. In
addition, wherever possible, the same reference numbers will be
used throughout the drawings and the specification to refer to the
same or like parts.
[0029] The embodiments of the present invention can be supported by
standard documents disclosed for at least one of wireless access
systems such as the institute of electrical and electronics
engineers (IEEE) 802, 3rd generation partnership project (3GPP),
3GPP long term evolution (3GPP LTE), LTE-advanced (LTE-A), and
3GPP2 systems. For steps or parts of which description is omitted
to clarify the technical features of the present invention,
reference may be made to these documents. Further, all terms as set
forth herein can be explained by the standard documents.
[0030] The following technology can be used in various wireless
access systems such as systems for code division multiple access
(CDMA), frequency division multiple access (FDMA), time division
multiple access (TDMA), orthogonal frequency division multiple
access (OFDMA), single carrier frequency division multiple access
(SC-FDMA), etc. CDMA may be implemented by a radio technology such
as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may
be implemented by a radio technology such as global system for
mobile communications (GSM)/general packet radio service
(GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA may be
implemented by a radio technology such as IEEE 802.11 (Wi-Fi), IEEE
802.16 (WiMAX), IEEE 802.20, evolved-UTRA (E-UTRA), etc. UTRA is a
part of universal mobile telecommunication system (UMTS). 3GPP LTE
is a part of evolved-UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs
OFDMA for downlink and SC-FDMA for uplink. LTE-A is an evolution of
3GPP LTE. WiMAX can be explained by the IEEE 802.16e specification
(wireless metropolitan area network (WirelessMAN)-OFDMA reference
system) and the IEEE 802.16m specification (WirelessMAN-OFDMA
advanced system). For clarity, the present disclosure focuses on
3GPP LTE and LTE-A systems. However, the technical features of the
present invention are not limited thereto.
[0031] The structure of a radio frame will now be described with
reference to FIG. 1.
[0032] In a cellular orthogonal frequency division multiplexing
(OFDM) wireless packet communication system, uplink (UL)/downlink
(DL) data packets are transmitted in units of subframes. One
subframe is defined as a predetermined time period including a
plurality of OFDM symbols. 3GPP LTE supports the structure of a
type 1 radio frame applicable to frequency division duplex (FDD)
and the structure of a type 2 radio frame applicable to time
division duplex (TDD).
[0033] FIG. 1(a) is a diagram illustrating the structure of the
type 1 radio frame. A DL radio frame is divided into 10 subframes
each including two slots in the time domain. A time during which
one subframe is transmitted is defined as a transmission time
interval (TTI). For example, one subframe may be 1 ms long and one
slot may be 0.5 ms long. One slot includes a plurality of OFDM
symbols in the time domain and a plurality of resource blocks (RBs)
in the frequency domain. Since the 3GPP LTE system uses OFDMA on
DL, an OFDM symbol is one symbol period. The OFDM symbol may be
called an SC-FDMA symbol or symbol period. An RB is a resource
allocation unit including a plurality of contiguous subcarriers in
one slot.
[0034] The number of OFDM symbols included in one slot may be
changed according to the configuration of a cyclic prefix (CP).
There are two types of CPs, extended CP and normal CP. For example,
if each OFDM symbol is configured to include a normal CP, one slot
may include 7 OFDM symbols. If each OFDM symbol is configured to
include an extended CP, the length of an OFDM symbol is increased
and thus the number of OFDM symbols included in one slot is less
than that in the case of a normal CP. In the case of the extended
CP, for example, one slot may include 6 OFDM symbols. If a channel
state is unstable, as is the case when a UE moves fast, the
extended CP may be used in order to further reduce inter-symbol
interference.
[0035] In the case of the normal CP, since one slot includes 7 OFDM
symbols, one subframe includes 14 OFDM symbols. The first two or
three OFDM symbols of each subframe may be allocated to a physical
downlink control channel (PDCCH) and the remaining OFDM symbols may
be allocated to a physical downlink shared channel (PDSCH).
[0036] FIG. 1(b) illustrates the structure of the type 2 radio
frame. The type 2 radio frame includes two half frames, each half
frame including 5 subframes, a DL pilot time slot (DwPTS), a guard
period (GP), and a UL pilot time slot (UpPTS). One subframe is
divided into two slots. The DwPTS is used for initial cell search,
synchronization, or channel estimation at a UE, and the UpPTS is
used for channel estimation and UL transmission synchronization
with a UE at an eNB. The GP is used to cancel UL interference
between UL and DL, caused by the multi-path delay of a DL signal.
One subframe includes two slots irrespective of the type of a radio
frame.
[0037] The structures of radio frames are only exemplary.
Accordingly, the number of subframes in a radio frame, the number
of slots in a subframe, and the number of symbols in a slot may be
changed in various manners.
[0038] FIG. 2 illustrates a resource grid in a DL slot. A DL slot
has 7 OFDM symbols in the time domain and an RB includes 12
subcarriers in the frequency domain, which does not limit the
present invention. For example, a DL slot includes 7 OFDM symbols
in a subframe with normal CPs, whereas a DL slot includes 6 OFDM
symbols in a subframe with extended CPs. Each element of the
resource grid is referred to as a resource element (RE). An RB
includes 12.times.7 REs. The number of RBs in a DL slot, N.sup.DL,
depends on a DL transmission bandwidth. A UL slot may have the same
structure as a DL slot.
[0039] FIG. 3 is a diagram illustrating the structure of a DL
subframe. Up to three OFDM symbols at the start of the first slot
of a DL subframe are used as a control region to which control
channels are allocated and the other OFDM symbols of the DL
subframe are used as a data region to which a PDSCH is allocated.
DL control channels used in the 3GPP LTE system include a physical
control format indicator channel (PCFICH), a physical downlink
control channel (PDCCH), and a physical hybrid automatic repeat
request (HARQ) indicator channel (PHICH). The PCFICH is located in
the first OFDM symbol of a subframe, carrying information about the
number of OFDM symbols used for transmission of control channels in
the subframe. The PHICH delivers a HARQ acknowledgment/negative
acknowledgment (ACK/NACK) signal as a response to a UL
transmission. Control information carried on the PDCCH is called
downlink control information (DCI). The DCI includes UL scheduling
information, DL scheduling information, or UL transmit power
control commands for UE groups. The PDCCH delivers information
about resource allocation and a transport format for a downlink
shared channel (DL-SCH), resource allocation information about an
uplink shared channel (UL-SCH), paging information of a paging
channel (PCH), system information on the DL-SCH, information about
resource allocation for a higher-layer control message such as a
random access response transmitted on the PDSCH, a set of transmit
power control commands for individual UEs of a UE group, transmit
power control information, voice over Internet protocol (VoIP)
activation information, etc. A plurality of PDCCHs may be
transmitted in the control region. A UE may monitor a plurality of
PDCCHs. A PDCCH is formed by aggregating one or more consecutive
control channel elements (CCEs). A CCE is a logical allocation unit
used to provide a PDCCH at a coding rate based on the state of a
radio channel. A CCE includes a plurality of resource element
groups. The format of a PDCCH and the number of available bits for
the PDCCH are determined according to the relationship between the
number of CCEs and a coding rate provided by the CCEs. An eNB
determines a PDCCH format according to DCI transmitted to a UE and
adds a cyclic redundancy check (CRC) to control information. The
CRC is masked by an identifier (ID) known as a Radio Network
Temporary Identifier (RNTI) according to the owner or usage of the
PDCCH. If the PDCCH is destined for a specific UE, the CRC may be
masked by a cell-RNTI (C-RNTI) of the UE. If the PDCCH carries a
paging message, the CRC thereof may be masked by a paging indicator
identifier (P-RNTI). If the PDCCH carries system information (more
particularly, a system information block (SIB), the CRC thereof may
be masked by a system information ID and a system information RNTI
(SI-RNTI). To indicate that the PDCCH carries a random access
response to a random access preamble transmitted by a UE, the CRC
thereof may be masked by a random access-RNTI (RA-RNTI).
[0040] FIG. 4 is a diagram illustrating the structure of a UL
subframe. The UL subframe is divided into a control region and a
data region in the frequency domain. A physical uplink control
channel (PUCCH) including uplink control information (UCI) is
allocated to the control region and a physical uplink shared
channel (PUSCH) including user data is allocated to the data
region. To maintain single-carrier properties, a UE does not
transmit a PUSCH and a PUCCH simultaneously. A PUCCH for one UE is
allocated to an RB pair in a subframe. The RBs belonging to the RB
pair occupy different subcarriers in two slots. Thus it is said
that the RB pair allocated to the PUCCH is frequency-hopped over a
slot boundary.
DCI Formats
[0041] Current LTE-A (release 10) defines DCI formats 0, 1, 1A, 1B,
1C, 1D, 2, 2A, 2B, 2C, 3, 3A, and 4. DCI formats 0, 1A, 3, and 3A
have the same message size to reduce the number of blind decoding
procedures as described later. According to the usages of control
information transmitted in these DCI formats, the DCI formats are
classified into i) DCI formats 0 and 4 used for a UL grant, ii) DCI
formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, and 2C used for DL scheduling
assignment, and iii) DCI formats 3 and 3A used for transmit power
control (TPC) commands
[0042] DCI format 0 used for transmission of a UL grant may include
a carrier indicator required for later-described carrier
aggregation, an offset that differentiates DCI format 0 from DCI
format 1A (flag for format 0/format 1A differentiation), a
frequency hopping flag indicating whether frequency hopping applies
to UL PUSCH transmission, resource block assignment information
about allocation of RBs to PUSCH transmission of a UE, a modulation
and coding scheme (MCS), a new data indicator used to empty a
buffer for initial transmission in relation to a HARQ process, a
TPC command for a scheduled PUSCH, cyclic shift for a DMRS and an
orthogonal code cover, a UL index required for time division
duplexing (TDD) operation, and channel quality indicator (CQI)
request (or channel state information (CSI) request) information.
Because DCI format 0 uses synchronous HARQ, DCI format 0 does not
include a redundancy version, compared to the DCI formats related
to DL scheduling assignment. If cross carrier scheduling is not
used, the carrier indicator is not included in the DCI format.
[0043] DCI format 4 has been newly added to LTE-A release 10, with
the aim to support spatial multiplexing for UL transmission.
Compared to DCI format 0, DCI format 4 further includes spatial
multiplexing information, thus having a relatively large message
size. In addition to control information included in DCI format 0,
DCI format 4 further includes other control information. That is,
DCI format 4 further includes an MCS for a second transport block,
precoding information for multiple input multiple output (MIMO)
transmission, and sounding reference signal (SRS) request
information. Because DCI format 4 is greater than DCI format 0 in
size, DCI format 4 does not include the flag for format 0/format 1A
differentiation.
[0044] Among DCI formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, and 2C
related to DL scheduling assignment, DCI formats 1, 1A, 1B, 1C, and
2C do not support spatial multiplexing, whereas DCI formats 2, 2A,
2B, and 2C support spatial multiplexing.
[0045] DCI format 1C supports only contiguous frequency allocation
as a compact DL assignment. Compared to other DCI formats, DCI
format 1C does not include the carrier offset and the redundancy
version.
[0046] DCI format 1A is used for DL scheduling and a random access
procedure. DCI format 1A may include a carrier indicator, an
indicator indicating whether distributed DL transmission is used,
PDSCH resource allocation information, an MCS, a redundancy
version, a HARQ process number indicating a processor used for soft
combining, a new data indicator used to empty a buffer for initial
transmission in relation to a HARQ process, a TPC command for a
PUCCH, a UL index required for TDD operation, etc.
[0047] Control information of DCI format 1 is mostly similar to
control information of DCI format 1A except that DCI format 1A is
related to contiguous resource allocation and DCI format 1 supports
non-contiguous resource allocation. Accordingly, DCI format 1
further includes a resource allocation header, thereby increasing
control signaling overhead as a trade-off of an increase in
resource allocation flexibility.
[0048] DCI formats 1B and 1D are common in that they further
include precoding information, compared to DCI format 1. DCI format
1B includes precoding matrix index (PMI) confirmation and DCI
format 1D carries DL power offset information. Other control
information included in DCI formats 1B and 1D is mostly identical
to control information of DCI format 1A.
[0049] DCI formats 2, 2A, 2B, and 2C basically include most of the
control information included in DCI format 1A and further include
spatial multiplexing information. The spatial multiplexing
information includes an MCS for a second transport block, a new
data indicator, and a redundancy version.
[0050] DCI format 2 supports closed-loop spatial multiplexing and
DCI format 2A supports open-loop spatial multiplexing. Both DCI
formats 2 and 2A include precoding information. DCI format 2B
supports dual-layer spatial multiplexing combined with beamforming
and further includes cyclic shift information for a DMRS. DCI
format 2C is an extension of DCI format 2B, supporting spatial
multiplexing of up to 8 layers.
[0051] DCI formats 3 and 3A may be used to support TPC information
included in the DCI formats used for transmission of a UL grant and
DL scheduling assignment, that is, to support semi-persistent
scheduling. A 1-bit command is used per UE in DCI format 3 and a
2-bit command is used per UE in DCI format 3A.
[0052] One of the above-described DCI formats may be transmitted on
one PDCCH and a plurality of PDCCHs may be transmitted in the
control region. A UE may monitor a plurality of PDCCHs.
PDCCH Processing
[0053] CCEs, which are contiguous logical allocation units, are
used to map PDCCHs to REs. One CCE includes a plurality of (e.g. 9)
resource element groups (REGs), each REG having four adjacent REs
except for RS REs.
[0054] The number of CCEs required for a specific PDCCH depends on
DCI payload indicating control information size and on cell
bandwidth, a channel coding rate, etc. Specifically, the number of
CCEs for a specific PDCCH may be defined according to a PDCCH
format, as illustrated in Table 1.
TABLE-US-00001 TABLE 1 PDCCH Number of Number of Number of format
CCEs REGs PDCCH bits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576
[0055] As described before, one of the above four formats is used
for a PDCCH, which is not known to a UE. Therefore, the UE should
decode the PDCCH without knowledge of the PDCCH format. This is
called blind decoding. However, because decoding of all possible DL
CCEs for each PDCCH format may impose a great constraint on the UE,
a search space is defined in consideration of scheduler
restrictions and the number of decoding attempts.
[0056] Namely, a search space is a set of candidate PDCCHs formed
by CCEs that the UE is supposed to attempt to decode at a given
aggregation level. Aggregation levels and the number of PDCCH
candidates may be defined as follows.
TABLE-US-00002 TABLE 2 Search space Aggregation Size Number of
PDCCH level (in CCEs) candidates UE-specific 1 6 6 2 12 6 4 8 2 8
16 2 Common 4 16 4 8 16 2
[0057] As noted from Table 2, there are four aggregation levels and
thus the UE has a plurality of search spaces at each aggregation
level. Search spaces may be classified into a UE-specific search
space and a common search space. The USS is configured for specific
UEs. Each of the UEs may monitor the UE-specific search space (may
attempt to decode a set of PDCCH candidates according to possible
DCI formats) and verify an RNTI masked with a PDCCH and a CRC of
the PDCCH. If the RNTI and CRC are valid, the UE may acquire
control information.
[0058] The common search space is designed for the case in which a
plurality of UEs or all UEs need to receive a PDCCH for dynamic
scheduling of system information or a paging message. Nonetheless,
the common search space may be used for a specific UE depending on
resource management. The common search space may overlap with the
UE-specific search space.
[0059] A search space may be determined by Equation 1 .
L{Y.sub.k+m')mod.left brkt-bot.N.sub.CCE,k/L.right brkt-bot.}+i
[Equation 3]
where L is an aggregation level, Y.sub.k is a variable determined
by an RNTI and subframe number k, and m' is the number of PDCCH
candidates. If carrier aggregation is used, m'=m+M.sup.(L)n.sub.CI
and otherwise, m'=m. Here, m=0, . . . , M.sup.(L)-1 where M.sup.(L)
is the number of PDCCH candidates. N.sub.CCE,k is the total number
of CCEs in the control region of a k-th subframe and i indicates an
individual CCE in a PDCCH candidate (i=0, . . . , L-1). In the
common search space, Y.sub.k is always 0.
[0060] FIG. 5 illustrates a UE-specific search space (shaded) at
each aggregation level, as defined by Equation 1. Here, carrier
aggregation is not adopted and N.sub.CCE,k is set to 32, for
convenience of description.
[0061] FIGS. 5(a), 5(b), 5(c), and 5(d) illustrate UE-specific
search spaces at aggregation levels 1, 2, 4, and 8, respectively.
In FIG. 5, numbers indicate CCE numbers. As described before, the
start CCE of a search space at each aggregation level is determined
by an RNTI and subframe number k. For a UE, the start CCE of a
search space may be different in the same subframe according to an
aggregation level due to a modulo function and L. In addition, the
start CCE of a search space is always a multiple of an aggregation
level due to L. By way of example, Y.sub.k is CCE 18. The UE
attempts to sequentially decode CCEs in units of CCEs determined by
an aggregation level, starting from the start CCE. For example, (b)
of FIG. 5, the UE attempts to decode CCEs in units of two CCEs
according to an aggregation level, starting from CCE 4 which is the
start CCE.
[0062] As described above, the UE attempts to perform decoding in a
search space. The number of decoding procedures is determined by a
DCI format and a transmission mode indicated by radio resource
control (RRC) signaling. If carrier aggregation is not used, the UE
needs to attempt a maximum of 12 decoding procedures in a common
search space, in consideration of two DCI sizes (DCI format
0/1A/3/3A and DCI format 1C) for each of six PDCCH candidates. In a
UE-specific search space, the UE needs to attempt a maximum of 32
decoding procedures, in consideration of two DCI sizes for each of
16 PDCCH candidates (6+6+2+2=16).
[0063] Meanwhile, if carrier aggregation is used, the maximum
number of decoding procedures is further increased because as many
decoding procedures as the number of DL resources (component
carriers) are added for a UE-specific search space and DCI format
4.
Reference Signal (RS)
[0064] In a wireless communication system, a packet is transmitted
through a radio channel and thus the packet may be distorted during
transmission. To receive a signal successfully, a receiver should
compensate for the distortion of the received signal using channel
information. To obtain the channel information, a transmitter
transmits a signal known to both the transmitter the receiver and
the receiver acquires the channel information based on the
distortion of the signal received through the radio channel. This
signal is called a pilot signal or an RS.
[0065] In the case of data transmission and reception using
multiple antennas, a channel states between transmit antennas and
receive antennas should be discerned in order to correctly receive
a signal. Accordingly, an RS should be transmitted through each
transmit antenna, more specifically, each antenna port.
[0066] RSs may be divided into UL RSs and DL RSs. In the current
LTE system, the UL RSs include:
[0067] i) Demodulation reference signal (DMRS) used for channel
estimation for coherent demodulation of information transmitted
through a PUSCH and a PUCCH; and
[0068] ii) Sounding reference signal (SRS) used for an eNB or a
network to measure the quality of a UL channel in a different
frequency.
[0069] The DL RSs include:
[0070] i) Cell-specific reference signal (CRS) shared among all UEs
in a cell;
[0071] ii) UE-specific RS dedicated to a specific UE;
[0072] iii) DM-RS used for coherent demodulation when a PDSCH is
transmitted;
[0073] iv) Channel State Information-Reference Signal (CSI-RS) used
for transmitting CSI, when DL DM-RSs are transmitted;
[0074] v) Multimedia broadcast single frequency network (MBSFN) RS
used for coherent demodulation of a signal transmitted in MBSFN
mode; and
[0075] vi) Positioning RS used to estimate geographical position
information of a UE.
[0076] RSs may be divided into two types according to purposes
thereof: RSs for channel information acquisition and RSs for data
demodulation. Since the purpose of the former is to cause the UE to
acquire DCI, the RSs for channel information acquisition should be
transmitted in a broad band and a UE that does not receive DL data
in a specific subframe should receive the RSs. The RSs for channel
information acquisition are also used in a situation such as
handover. The RSs for data demodulation are RSs that are
transmitted by an eNB to a corresponding resource together with DL
data. A UE can demodulate the data by measuring a channel using the
RSs for data demodulation. The RSs for data demodulation should be
transmitted in a data transmission area.
[0077] The CRS is used for two purposes, that is, channel
information acquisition and data demodulation. The UE-specific RS
is used only for data demodulation. The CRS is transmitted in every
subframe in a broad band and CRSs for up to four antenna ports are
transmitted according to the number of transmit antennas of an
eNB.
[0078] For example, if the number of transmit antennas of an eNB is
2, CRSs for antenna ports 0 and 1 are transmitted. In the case of
four transmit antennas, CRSs for antenna ports 0 to 3 are
respectively transmitted.
[0079] FIG. 6 illustrates patterns in which CRSs and DRSs are
mapped to a DL RB pair, as defined in a legacy 3GPP LTE system
(e.g. a Release-8 system). A DL RB pair as an RS mapping unit may
be expressed as one subframe in time by 12 subcarriers in
frequency. That is, an RB pair includes 14 OFDM symbols in the time
domain in the case of the normal CP (see FIGS. 5(a) and 12 OFDM
symbols in the time domain in the case of the extended CP (FIG.
6(b).
[0080] FIG. 6 illustrates the positions of RSs on an RB pair in a
system where an eNB supports four transmit antennas. In FIG. 5, REs
expressed by reference numerals `0`, `1`, `2`, and `3` illustrates
the positions of CRSs for antenna ports 0, 1, 2, and 3,
respectively, and REs expressed by `D` denote the positions of
DRSs.
Demodulation Reference Signal (DMRS)
[0081] A DMRS is an RS defined for the purpose of causing a UE to
perform channel estimation for a PDSCH. The DMRS may be used in
transmission ports 7, 8, and 9. Initially, the DMRS has been
defined for a single layer of antenna port 5 and, thereafter, the
use of the DMRS has been extended for spatial multiplexing of a
maximum of 8 layers. As can be appreciated from its other name
UE-specific RS, the DMRS is transmitted only for one specific UE.
Therefore, the DMRS may be transmitted only in an RB in which a
PDSCH for the specific UE is transmitted.
[0082] The DMRS for up to 8 layers are generated as follows. The
DMRS may be transmitted by mapping a reference-signal sequence r(m)
generated by Equation 5 to complex-valued modulation symbols
a.sub.k,l.sup.(p) according to Equation 6. FIG. 7 illustrates
antenna ports 7 to 10 as a result of mapping the DMRS to a resource
grid on a subframe in the case of a normal CP according to Equation
5.
r ( m ) = 1 2 ( 1 - 2 c ( 2 m ) ) + j 1 2 ( 1 - 2 c ( 2 m + 1 ) ) ,
m = { 0 , 1 , , 12 N RB max , DL - 1 normal CP 0 , 1 , , 16 N RB
max , DL - 1 extended CP [ Equation 5 ] ##EQU00001##
where r(m) denotes an RS sequence, c(i) denotes a pseudo random
sequence, and N.sub.RB.sup.max,DLdenotes the maximum number of RBs
of DL bandwidth.
a k , l ( p ) = w p ( l ' ) r ( 3 l ' N RB max , DL + 3 n PRB + m '
) w p ( i ) = { w _ p ( i ) ( m ' + n PRB ) mod 2 = 0 w _ p ( 3 - i
) ( m ' + n PRB ) mod 2 = 1 k = 5 m ' + N sc RB n PRB + k ' k ' { 1
p .di-elect cons. { 7 , 8 , 11 , 13 } 0 p .di-elect cons. { 9 , 10
, 12 , 14 } l = { l ' mod 2 + 2 for special subframe configurations
3 , 4 , 8 , and 9 l ' mod 2 + 2 + 3 l ' / 2 ] for special subframe
configurations 1 , 2 , 6 , and 7 l ' mod 2 + 5 for non - special
subframes l ' { 0 , 1 , 2 , 3 for n s mod 2 = 0 and special
subframe configurations 1 , 2 , 6 , and 7 0 , 1 for n s mod 2 = 0
and special subframe configurations orther than 1 , 2 , 6 , and 7 2
, 3 for n s mod 2 = 1 and special subframe configurations orther
than 1 , 2 , 6 , and 7 m ' = 0 , 1 , 2 [ Equation 6 ]
##EQU00002##
[0083] As can be seen from Equation 6, an orthogonal sequence
w.sub.p(i) as illustrated in Table 5 is applied to the RS sequence
according to an antenna port during mapping to a complex modulation
symbol.
TABLE-US-00003 TABLE 5 Antenna port .sup.p [ w.sub.p(0) w.sub.p(1)
w.sub.p(2) w.sub.p(3)] 7 [+1 +1 +1 +1] 8 [+1 -1 +1 -1] 9 [+1 +1 +1
+1] 10 [+1 -1 +1 -1] 11 [+1 +1 -1 -1] 12 [-1 -1 +1 +1] 13 [+1 -1 -1
+1] 14 [-1 +1 +1 -1]
[0084] A UE may perform channel estimation using a DMRS by a
different method according to a spreading factor (2 or 4).
Referring to Table 5, since orthogonal sequences are repeated in
the form of [a b a b] in antenna ports 7 to 10, a spreading factor
is 2 and, in antenna ports 11 to 14, the spreading factor is 4. If
the spreading factor is 2, the UE may perform channel estimation
through time interpolation after despreading a DMRS of the first
slot and a DMRS of a second slot to spreading factor 2. When the
spreading factor is 4, the UE may perform channel estimation by
simultaneously despreading DMRSs in an entire subframe to spreading
factor 4.
[0085] The above-described channel estimation according to the
spreading factor can obtain gain caused by application of time
interpolation in high mobility and obtain gain in a decoding time
caused by the possibility of despreading to a DMRS of the first
slot, when the spreading factor is 2. In addition, when the
spreading factor is 4, more UEs or ranks can be supported.
[0086] FIG. 8 will now be described in terms of DMRS overhead. FIG.
8 illustrates mapping in a subframe of DMRSs for antenna ports 7 to
14. As illustrated in FIG. 8, there are code divisional
multiplexing (CDM) group 1 (or a first antenna port set) and CDM
group 2 (or a second antenna port set) according to a DMRS mapping
position in a resource grid. On REs corresponding to CDM group 1,
DMRSs are transmitted through antenna ports 7, 8, 11, and 13 and,
on REs corresponding to CDM group 2, DMRSs are transmitted through
antenna ports 9, 10, 12, and 14. That is, DMRSs are transmitted on
the same REs through antenna ports included in one CDM group. If
DMRSs are transmitted using only antenna ports corresponding to CDM
group 1, resources necessary for DMRSs are 12 REs, that is, DMRS
overhead is 12 REs. Similarly, when antenna ports corresponding to
CDM group 2 are used, DMRS overhead is 24 REs.
[0087] In an LTE system after Release 11, an enhanced-PDCCH
(E-PDCCH) is considered as a solution to PDCCH capacity shortage
caused by coordinated multi-point (CoMP) transmission and
multi-user (MU)-MIMO and to PDCCH performance deterioration caused
by inter-cell interference. In the E-PDCCH, DMRS based channel
estimation can be performed to acquire precoding gain etc. as
opposed to a conventional CRS based PDCCH.
[0088] In relation to transmission of this E-PDCCH, the present
invention proposes that an antenna port and/or a scrambling
sequence (or an initial value of the scrambling sequence) of a DMRS
used when an eNB transmits the E-PDCCH to a specific UE be changed
according to resources associated with E-PDCCH transmission (e.g. a
PRB pair, a subframe, a starting enhanced CCE (eCCE) of a candidate
position, an index of a subset in the PRB pair).
[0089] That is, when an eNB transmits an E-PDCCH to a specific UE,
a parameter associated with the DMRS for the E-PDCCH may be
configured with respect to each E-PDCCH related resource. Although
the DMRS parameter may be, for example, antenna ports and a
scrambling sequence (or an initial value of the scrambling
sequence) as described previously, the present invention is not
limited thereto and other parameters associated with the DMRS may
be used. The starting eCCE of the candidate position refers to a
CCE having the lowest index among L CCEs constituting a
corresponding position at a specific candidate position of an
aggregation level L formed by aggregating L CCEs. (In the case of a
localized E-PDDCH,) L eCCEs constituting a single E-PDCCH may be
transmitted with the same DMRS antenna port or scrambling sequence.
The subset in the PRB pair refers to a subset of REs formed by
splitting REs belonging to one PRB pair into two or more subsets. A
plurality of E-PDCCHs may be multiplexed in a single PRB pair using
different subsets. (For example, one PRB pair may include 4 eCCEs,
each having 4 enhanced REGs (eREGs). A localized E-PDCCH may be
transmitted in units of an eCCE and a distributed E-PDCCH may be
transmitted by forming one eCCE with eREGs belonging to different
PRB pairs. Plural eCCEs may be used for one E-PDCCH (or DCI)
transmission according to an aggregation level). In addition, the
scrambling sequence (or the initial value of the scrambling
sequence) may be generated as a cell ID, a serving cell ID (SCID)
field, or a combination of the cell ID, the SCID, and other various
parameters. The scrambling sequence may be changed by varying all
or some of these parameters.
[0090] One embodiment related a PRB pair among the above-mentioned
resources associated with E-PDCCH transmission, will now be
described. According to the present invention, when an E-PDCCH is
transmitted using at least one PRB pair among a plurality of PRB
pairs, a DMRS parameter for the E-PDCCH is configured for each of
the plurality of PRB pairs (The plurality of PRB pairs may be
referred to as an E-PDCCH set, and a UE may detect a candidate by
blind decoding from the E-PDCCH set and determine whether the
E-PDCCH is actually transmitted via the candidate through blind
decoding). The plurality of PRB pairs may include one or more PRB
pairs for localized E-PDCCH transmission and/or one or more PRB
pairs for distributed E-PDCCH transmission, as illustrated in FIG.
11.
[0091] In consideration of the above description, according to the
proposal of the present invention, the DMRS parameter (e.g. a DMRS
port and/or scrambling sequence parameter) may be configured with
respect to each E-PDCCH set (or E-PDCCH sets) signaled for E-PDCCH
transmission and the E-PDCCH set is for a localized E-PDCCH or is
for a distributed E-PDCCH.
[0092] That is, when a DMRS parameter is a scrambling sequence (or
an initial value of the scrambling sequence), the scrambling
sequence (or the initial value of the scrambling sequence) is
configured with respect to each PRB pair set. The scrambling
sequence (or the initial value of the scrambling sequence)
configured with respect to each PRB pair set may be transmitted to
a UE through higher layer signaling (RRC signaling). If the DMRS
parameter is antenna ports, the antenna ports may be configured
with respect to each PRB pair set for localized/distributed E-PDCCH
transmission. For example, as illustrated in later-described FIG.
11, for one or more PRB pair sets for localized E-PDCCH
transmission, antenna ports {7, 8, 9, 10} may be configured and,
for a PRB pair set for distributed E-PDCCH transmission, antenna
ports {7, 9, 7, 9} may be configured. As is the case of the
scrambling sequence, information regarding the antenna ports
associated with a PRB pair may be transmitted to the UE through
higher layer signaling.
[0093] FIG. 9 illustrates assignment of different antenna ports to
a PRB pair set for localized E-PDCCH transmission and a PRB pair
set for distributed E-PDCCH transmission in the case in which a
DMRS parameter (especially, antenna ports) is configured for one or
more PRB pairs.
[0094] As described above, E-PDCCH transmission may be divided into
localized transmission and distributed transmission according to a
transmission scheme. E-PDCCH transmission schemes may be
differentiated according to whether one eCCE is dividedly
transmitted on a plurality of PRB pairs. That is, division
transmission of one eCCE on a plurality of PRB pairs may be
distributed transmission and a resource set dividedly defined from
one eCCE may be an eREG. Antenna ports used in each resource set
may be differently configured. When an antenna port configuration
is applied in association with the transmission scheme, the antenna
port configuration may differ according to the transmission
scheme.
[0095] Specifically, referring to FIG. 9, it is assumed that one
PRB pair includes 8 eREGs and two eREGs having consecutive indexes
constitutes one eCCE in localized transmission. The eREGs in one
PRB pair may be defined by frequency division multiplexing (FDM),
time division multiplexing (TDM), or FDM and TDM or may be defined
by an interleaving scheme for interference randomization.
Configuration of one eCCE with non-consecutive two eREGs in
localized/distributed transmission is also embraced in the scope of
the present invention.
[0096] Referring to FIG. 9 (a), localized transmission is
configured by antenna ports {7, 8, 9, 10} starting from an eCCE of
a low index and distributed transmission is configured by antenna
ports {7, 7, 7, 7}. In consideration of assignment of antenna ports
in units of an eREG, antenna ports {7, 7, 8, 8, 9, 9, 10, 10, 11,
11} are allocated for localized transmission and antenna ports {7,
7, 7, 7, 7, 7, 7, 7} are allocated for distributed
transmission.
[0097] In FIG. 9(b), antenna ports allocated in units of an eREG
are illustrated. It is assumed that for localized transmission,
antenna ports {7, 7, 9, 9, 8, 8, 10, 10} are allocated and, for
distributed transmission, antenna ports {7, 9, 7, 9, 7, 9, 7, 9}
are allocated. Assuming that antenna port allocation is determined
in units of an eCCE for localized transmission, allocation of
antenna ports {7, 9, 8, 10} may be signaled or pre-configured. If
it is desired to use mapping in units of an eCCE even for
distributed transmission, a method for configuring antenna ports
{7, 9, 7, 9, 7, 9, 7, 9} of FIG. 9(b) as {7, 7, 9, 9, 7, 7, 9, 9}
may be considered and antenna ports {7, 9, 7, 9} are mapped in
eCCEs.
[0098] The relationship between an eCCE (or eREG) in a PRB pair and
an antenna port may be preconfigured per transmission scheme and a
PRB pair set to which each scheme is applied may be signaled to a
UE.
[0099] FIG. 10 exemplarily illustrates a change of pattern of a
DMRS parameter to a specific pattern in the case in which a DMRS
parameter is configured in units of a PRB (or a PRB pair). That is,
an eNB may inform a UE of a change pattern of an antenna port
and/or a scrambling sequence of a DMRS through higher layer
signaling. As one method, the eNB may inform the UE of an antenna
port and/or a scrambling sequence to be used at a specific position
and the UE may operate to derive antenna ports and/or scrambling
sequences to be used at the other positions through a predetermined
rule from the known antenna port and/or scrambling sequence. It may
be understood that the eNB assigns the UE an offset value for a
position at which a pattern is started in a situation in which an
antenna port and/or a scrambling sequence of a DMRS to be used at
each position is determined as a predetermined pattern.
[0100] This will be described in detail with reference to FIG. 10.
In FIG. 10(a), each RB (RB pair) alternately uses antenna ports 7,
8, 9, and 10 when an SCID is fixed to 0 and this may be represented
that RB nx uses antenna port (7+(x mod 4). In this case, assuming
that an offset value is set to 0, this may represent that RB nx
uses antenna port (7+(x+offset) mod 4). Since antenna ports 7, 8,
9, and 10 are used in the above example, the total number of DMRS
antenna ports, M.sub.port, used by a corresponding UE to receive an
E-PDCCH is 4. M.sub.port may differ according to a UE and may also
be configured through a higher layer signal. In this case, an
antenna port of RB nx may be generalized as Equation 7.
(7+(x+offset) mod M.sub.port) [Equation 7 ]
[0101] FIG. 10(b) explains that RB nx uses an SCID
(floor(x/4)+offset) mod 2) in which an offset is set to 0.
[0102] Alternatively, an antenna port number used in each RB may be
expressed as a combination of an antenna port change period
Period.sub.port and a first used antenna port number
Start.sub.port. That is, an antenna port number may be expressed
such that antenna port (7+Start.sub.port) is used in first
Period.sub.port RBs and antenna port (7+Start.sub.port+1) is used
in next Period.sub.port RBs. Accordingly, an antenna port used in
RB nx may be expressed by Equation 8.
(7+((Start.sub.port+floor(x/Period.sub.port) mod M.sub.port)
[Equation 8]
[0103] When Equation 8 is applied, FIG. 10(a) corresponds to the
case in which Start.sub.port=0, Period.sub.port=1, and M.sub.port=4
and FIG. 10(c) corresponds to the case in which Start.sub.port=0,
Period.sub.port=2, and M.sub.port=4.
[0104] While the above description has been given under the premise
that a DMRS antenna port number and a scrambling sequence are
changed in each RB, this is exemplary and the DMRS antenna port
number and the scrambling sequence may differ according to a PRB
pair set, a starting eCCE of a candidate position, and/or a subset
in a PRB pair.
[0105] FIG. 11 exemplarily illustrates an antenna port
configuration for each UE based on Equation 8. Specifically, in
FIG. 11, antenna ports for UE1, UE2, and UE3 are configured when
Start.sub.port=0, 0, and 1 and Period.sub.port=1, 2, and 4,
respectively. As a result, a combination of UEs having the same
antenna port in a specific RB becomes different as illustrated in
FIG. 11. Accordingly, an eNB may variously select a possible
MU-MIMO pairing in each RB. For example, in RB n0 and RB n7, one of
UE1 and UE2 having the same antenna port is selected to perform
MU-MIMO with UE3, whereas in RB n1 and RB n6, one of UE3 and UE1
having the same antenna port is selected to perform MU-MIMO with
UE2. That is, various MU-MIMO pairing can be performed relative to
the case in which DMRS antenna ports are uniformly configured over
all RBs.
[0106] A pattern in which a DMRS antenna port and/or a scrambling
sequence to be used in each RB (or a PRB pair set, a starting CCE
of a candidate position, and/or a subset in an RB) is changed may
differ according to a C-RNTI allocated to a UE, a cell ID, and a
scrambling parameter of a CSI-RS and thus it is guaranteed that
each UE has a different pattern. In addition, an antenna port
pattern may be determined with priorities between parameters. For
example, priorities may be determined in order of a CSI-RS
scrambling parameter, a cell ID, and a C-RNTI and antenna port
assignment may be reconfigured using available parameters at a
reconfiguration message reception time. If a parameter
corresponding to priority is not available, a parameter with the
next priority may be used to determine the pattern. The above
parameters may be differently applied according to a transmission
form. For example, in localized transmission, a C-RNTI may be used
to determine an antenna port pattern and, when a shared RS is used,
the antenna port pattern may be determined based on a cell ID, a
virtual cell ID used in a DMRS or a CSI-RS, or a scrambling
parameter because a plurality of E-PDCCHs share the same antenna
port.
[0107] The above description has been given on the premise that the
number of REs available for an E-PDCCH in one PRB pair is
sufficient. However, the number of REs available for an E-PDCCH in
one PRB pair may be reduced in an extended CP of FDD/TDD, a
subframe (or a PRB pair set) in which a PBCH/SCH is transmitted, a
special subframe of TDD, or a subframe (or a PRB pair set) with
significant RS overhead such as CRS/CSI-RS/DMRS overhead.
[0108] In this way, if the amount of resources available for the
E-PDCCH is insufficient and an eCCE (or an eREG) is configured only
by available resources (i.e. if the eCCE (or eREG) is configured
only by REs used for E-PDCCH transmission), the positions of REs
constituting the eCCE (or eREG) in a PRB pair may differ according
to a subframe (or a PRB pair). Accordingly, the linkage between an
index of the eCCE (or eREG) in the PRB pair and an antenna port may
be predetermined (this may be transmitted through higher layer
signaling). If the number of eCCEs (or eREGs) is less than the
number of configured antenna ports per PRB pair, it is proposed
that only the available number of antenna ports be used starting
from a determined index (e.g. from a low index or from a high
index).
[0109] FIG. 12 illustrates the above example. In FIG. 12, it is
assumed that the number of resources available for an E-PDCCH in
each of shaded PRB pairs is reduced to half the available number of
resources in a normal PRB pair because the shaded PRB pairs include
the PBCH/SCH. Accordingly, if the number of eCCEs per PRB pair in a
normal PRB pair is 4, the number of eCCEs in the shade PRB pair is
reduced to 2 from 4. It is assumed that signaled or predefined
mapping of an eCCE to an antenna port for a corresponding UE is
determined in order of antenna ports {7, 8, 9, 10} starting from an
antenna port having a low index in a PRB pair. As in FIG. 9, it is
also assumed that two consecutive eREGs constitute one eCCE. In
consideration of mapping in units of an eREG, in a normal PRB pair
of the left side of FIG. 12, eREG-to-antenna port mapping of {7, 7,
8, 8, 9, 9, 10, 10} is performed and, in a PRB pair of the right
side of FIG. 12 in which the number of eCCEs is reduced to 2 from
4, eREG-to-antenna port mapping of {7, 7, 8, 8} may be
performed.
[0110] Similarly, in TDD, eCCE (or eREG)-to-antenna port mapping in
a normal subframe (or a subframe with sufficiently available
resources) for an E-PDCCH may be signaled or preconfigured and only
a part of antenna ports used for eCCE (or eREG)-to-antenna port
mapping may be used in a special subframe in which the available
number of resources is reduced. Further, when overhead is further
generated (e.g. due to an RS), only one antenna port (e.g. antenna
port {7}) may be used.
[0111] The above description may be interpreted in a logical domain
as follows. If all eCCEs (or eREGs) for an E-PDCCH are indexed,
eREG indexes 0 to 11 (eCCE indexes 0 to 5) may be derived with
respect to two PRB pairs and eCCE (or eREG)-to-antenna port mapping
in a PRB pair, that is, {7, 7, 8, 8, 9, 9, 10, 10} may be
interpreted starting from a resource set having the lowest index in
a PRB pair. For example, in FIG. 12, resource set indexes in a PRB
pair in which the PBCH/SCH is transmitted may be 8, 9, 10, and 11
and this may mean that antenna ports {7, 7, 8, 8} are mapped to
eREGs 8 to 11 by applying mapping of antenna ports {7, 7, 8, 8, 9,
9, 10, 10}.
[0112] As a method different from that described with reference to
FIG. 12, use of specific antenna ports among antenna ports mapped
when resources for an E-PDCCH are sufficient may be signaled. This
method may be used especially for interference coordination, RS
collision avoidance, etc.
[0113] For example, a network may determine priority for antenna
port mapping when resources for an E-PDCCH are sufficient and then
if the number of antenna ports is reduced, the network may
determine antenna ports based on the priority. In this case, a
plurality of priorities may be predetermined and a specific
priority may be selected based on a cell ID, a UE ID (C-RNTI), a
virtual cell ID, etc. The priorities will be transmitted through
higher layer signaling.
[0114] Alternatively, a method for configuring subsets for antenna
port assignment according to the number of antenna ports and
determining antenna port mapping to be used among subsets
corresponding to the reduced number of antenna ports based on a
cell ID, a UE ID (C-RNTI), a virtual cell ID, etc. may be used.
[0115] As described above, in the case of use of a shared RS and a
high aggregation level, the lesser number of antenna ports may be
used in one PRB pair, as is the case when the number of antenna
ports is reduced due to shortage of the amount of resources in a
PRB pair. The shared RS may be useful when decoding of plural
E-PDCCHs is performed through one antenna port and when CSI
feedback is incorrect or a common control signal is transmitted. In
a high aggregation level, a plurality of eCCEs (or eREGs) may be
used for one DCI transmission. If plural antenna ports are used,
since complexity of channel estimation increases, single antenna
port transmission is suitable. If the amount of resources in a PRB
pair is insufficient, for example, in a special subframe, since
assignment of multiple antenna ports to a corresponding PRB pair
generates unnecessary resource consumption, it is desirable to
allocate a number of antenna ports suitable for the amount of
resources.
[0116] In E-PDCCH transmission, RS collision with a neighboring
cell should be considered and, when RS collision occurs, a UE
especially located at a cell edge may decrease in E-PDCCH
performance. For example, this case is generated when a DMRS
antenna port for an E-PDCCH from a serving cell is equal to a DMRS
port used by a neighboring cell for a PDSCH. As one of methods for
solving this problem, different antenna ports may be allocated to
neighboring cells (or transmission points). However, this method
generates signaling overhead caused by UE-specific signaling. As
another method, when a lesser number of RSs is used for E-PDCCH
transmission, specific antenna ports (e.g. antenna ports 9 and 10)
may be configured to be used first in order to avoid RS collision.
For example, when one port per PRB pair is allocated, antenna port
9 or 10 may be used or antenna ports 9 and 10 may be repeated in
units of a resource set (e.g. an eREG or eCCE). In other words,
antenna ports different from frequently used antenna ports 7 and 8
during DMRS transmission for a PDSCH in a neighboring cell may be
generally used first. In this context, a more detailed description
will be given below by distinguishing between the case in which
resources for use of a shared RS/E-PDCCH are not sufficient and the
case in which a high aggregation level is used.
[0117] First, when resources for use of a shared RS/E-PDCCH are not
sufficient, specific antenna ports may be used first. For example,
as many antenna ports as the number of necessary RS antenna ports
may be allocated with priority of antenna ports 10, 9, 8, and 7. As
an example, antenna port 10 may be used when one antenna port is
allocated, antenna ports 9 and 10 may be used when two antenna
ports are allocated, and antenna ports 9, 10, and 8 may be used
when three antenna ports are allocated. Alternatively, if MU-MIMO
is not applied to a PDSCH transmission of a neighboring cell,
antenna ports may be selected by excluding antenna port 7 which is
mainly used, first. Furthermore, when only two of four antenna
ports are used, since antenna ports may be configured by a
combination of antenna ports belonging to different CDM groups
(e.g. antenna ports 7 and 9 or antenna ports 8 and 10) for power
amplification gain, a neighboring cell has a high probability of
using these antenna ports 7 and 9 and thus specific antenna ports 8
and 10 may be used.
[0118] Next, when a high aggregation level is used, a
representative antenna port may be used. An antenna port allocated
to an eCCE of the lowest index of eCCEs of a corresponding PRB pair
may be determined as the representative antenna port. That is,
antenna ports may be allocated such that antenna ports 9 and 10 are
arranged on the lowest index. If an antenna port of a specific eCCE
including the case of using the lowest index is selected as the
representative antenna port, antenna port 9 or 10 may be determined
as the representative antenna port using the same method. Antenna
ports allocated to a corresponding PRB pair may be {9, 10, 7, 8},
{10, 9, 7, 8}, {9, 10, 8, 7}, or {10, 9, 8, 7} when one PRB is
divided into four eCCEs. Alternatively, unlike the above
description, if a high aggregation level is configured, antenna
port 9 or 10 is used irrespective of an eCCE. Since collision
avoidance may be possible through scheduling in the case of
aggregation level 2, a high aggregation level may be 4 or more.
[0119] The above description has proposed that a DMRS configuration
per unit resource set (e.g. PRB pair (set), subset per PRB pair
(eCCE), etc.) for E-PDCCH transmission be determined through RRC
signaling. Such description (e.g. a UE may use a different DMRS
configuration per E-PDCCH transmission unit for E-PDCCH detection
and the DMRS configuration per transmission unit may be indicated
using RRC signaling) may be interpreted as two methods described
below. Hereinafter, for description, the terms physical domain and
logical domain will be used. The physical domain refers to resource
arrangement in OFDM symbol mapping and the logical domain refers to
resource arrangement for partial resources signaled for E-PDCCH
detection in the physical domain. FIG. 13 illustrates the
relationship between the physical domain the logical domain,
wherein the logical domain may be a domain in which resources
corresponding to a search space of an E-PDCCH are arranged. While
the above description has been given focusing upon a single domain,
the present invention is applicable to transmission using a
plurality of layers as illustrated in FIG. 13.
[0120] As the first interpretation, an eNB may determine a DMRS
configuration per unit resource in a physical domain and assign a
search space for E-PDCCH detection per UE. In this case, the eNB
may signal the DMRS configuration per resource unit in the physical
domain to each UE. The afore-proposed pattern signaling scheme may
be applied to signal the DMRS configuration per corresponding
resource, thereby reducing signaling overhead. FIG. 14(a)
illustrates the case in which plural antenna ports are configured
on one layer in a physical domain. Obviously, the number of layers
may increase and multiple DMRS parameters such as scrambling
sequence parameters may be configured.
[0121] Although it is assumed in FIG. 14(a) that one PRB pair is
divided into four subsets and one subset is used as a basic unit of
E-PDCCH transmission, the present invention may be applied when a
resource unit for E-PDCCH transmission is a PRB pair or multiple
PRB pairs. In FIG. 14, an eNB may indicate a pattern for antenna
ports used for each subset in a physical domain to a UE through RRC
signaling and a DMRS configuration for E-PDCCH detection may be
finally determined through signaling for a search space. The
pattern for antenna ports may be configured such that antenna ports
7, 8, 9, and 10 are repeated as in pattern signaling A in the left
of FIG. 14(a) or antenna ports 9, 10, 7, and 8 are repeated as in
pattern signaling B in the right of FIG. 14(a). In summary, a DMRS
configuration for an eCCE is signaled in the physical domain and
then a search space configuration is signaled.
[0122] As the second interpretation, a pattern for each resource
unit is signaled in a logical domain. That is, as illustrated in
FIG. 14(b), information about a search space is signaled in the
physical domain as in legacy LTE/LTE-A and then a pattern to be
used in a corresponding search space may be signaled in the logical
domain. While the above description has been exemplarily given
focusing upon configuration signaling for antenna ports, the
present invention may be applied even to a plurality of parameters
usable for a DMRS configuration, such as scrambling sequence
parameters.
[0123] FIG. 15 is a block diagram of a transmission point and a UE
according to an embodiment of the present invention.
[0124] Referring to FIG. 15, a transmission point 1510 according to
the present invention may include a reception module 1511, a
transmission module 1512, a processor 1513, a memory 1514, and a
plurality of antennas 1515. The transmission point 1510 supports
MIMO transmission and reception through the plural antennas 1515.
The reception module 1511 may receive signals, data, and
information on UL from the UE. The transmission module 1512 may
transmit signals, data, and information on DL to the UE. The
processor 1513 may control overall operation of the transmission
point 1510.
[0125] The processor 1513 of the transmission point 1510 according
to an embodiment of the present invention may process operations
necessary for above-described measurement reporting, handover,
random access, etc.
[0126] The processor 1513 of the transmission point 1510 may
process information received by the transmission point 1510 or
information to be transmitted from the transmission point 1510. The
memory 1514 may store processed information for a predetermined
time and may be replaced with a component such as a buffer (not
shown).
[0127] Referring to FIG. 15, a UE 1520 may include a reception
module 1521, a transmission module 1522, a processor 1523, a memory
1524, and a plurality of antennas 1525. The UE 1520 supports MIMO
transmission and reception through the plural antennas 1525. The
reception module 1521 may receive signals, data, and information on
DL from the transmission point. The transmission module 1522 may
transmit signals, data, and information on UL to the transmission
point. The processor 1523 may control overall operation of the UE
1520.
[0128] The processor 1523 of the UE 1520 according to an embodiment
of the present invention may process operations necessary for
above-described measurement reporting, handover, random access,
etc.
[0129] The processor 1523 of the UE 1520 may process information
received by the UE 1520 or information to be transmitted from the
UE 1520. The memory 1524 may store processed information for a
predetermined time and may be replaced with a component such as a
buffer (not shown).
[0130] The above transmission point and the UE may be configured to
implement the foregoing embodiments independently or implement two
or more of the embodiments simultaneously. For clarity, a repeated
description will be omitted herein.
[0131] The description of the transmission point 1510 in FIG. 15
may apply to a relay node as a DL transmission entity or a UL
reception entity and the description of the UE 1520 in FIG. 15 may
apply to the relay node as a DL reception entity or a UL
transmission entity.
[0132] The above-described embodiments of the present invention may
be achieved by various means, for example, hardware, firmware,
software, or a combination thereof.
[0133] In a hardware configuration, the methods according to the
embodiments of the present invention may be achieved by one or more
application specific integrated circuits (ASICs), digital signal
processors (DSP), digital signal processing devices (DSDPs),
programmable logic devices (PLDs), field programmable gate arrays
(FPGAs), processors, controllers, microcontrollers,
microprocessors, etc.
[0134] In a firmware or software configuration, the methods
according to the embodiments of the present invention may be
implemented in the form of a module, a procedure, a function, etc.
Software code may be stored in a memory unit and executed by a
processor. The memory unit is located at the interior or exterior
of the processor and may transmit and receive data to and from the
processor via various known means.
[0135] The detailed description of the exemplary embodiments of the
present invention is given to enable those skilled in the art to
realize and implement the present invention. While the present
invention has been described referring to the exemplary embodiments
of the present invention, those skilled in the art will appreciate
that many modifications and changes can be made to the present
invention without departing from the scope of the present
invention. For example, the constructions of the above-described
embodiments of the present invention may be used in combination.
Therefore, the present invention is not intended to limit the
embodiments disclosed herein but is to give a broadest range
matching the principles and new features disclosed herein.
[0136] The present invention may be embodied in other specific
forms than those set forth herein without departing from the spirit
and essential characteristics of the present invention. The above
description is therefore to be construed in all aspects as
illustrative and not restrictive. The scope of the invention should
be determined by reasonable interpretation of the appended claims
and all changes coming within the equivalency range of the
invention are intended to be within the scope of the invention. The
present invention is not intended to limit the embodiments
disclosed herein but is to give a broadest range matching the
principles and new features disclosed herein. In addition, claims
that are not explicitly cited in each other in the appended claims
may be presented in combination as an embodiment of the present
invention or included as a new claim by subsequent amendment after
the application is filed.
INDUSTRIAL APPLICABILITY
[0137] The above-described embodiments of the present invention are
applicable to various mobile communication systems.
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